Abstract

Ytterbium doped fiber lasers are known to be impacted by the creation of color centers during lasing so called photodarkening. This defect creation was investigated in a spectroscopic point of view, showing the presence of thulium traces (ppb) in the ytterbium doped fiber. Moreover, this contamination exhibit luminescence in the UV range under 976 nm excitation of the ytterbium-doped fiber. In adding more thulium to an ytterbium-doped fiber it was shown that thulium strongly impact the defects creation process, involved in photodarkening.

Schematic of up conversion processes in the ytterbium-thulium doped sample: The Yb emission [21] and Tm UV [19] and the visible - infrared [20] energy level diagram are depicted together with the luminescence transitions of Fig. 1 represented by green arrows.

Photo-induced absorption as function of time at 440 nm when excited with a 10W.m−2 power density laser at 976 nm (●: ytterbium doped sample and ▲ for ytterbium-thulium codoped sample). Inset: detail of the absorption evolution from 0 to 50 minutes.